1. Field of the Invention
The present invention relates to a multilayered ceramic capacitor to be used in the electronics field.
2. Description of the Prior Art
A multilayered ceramic capacitor has heretofore been produced by forming internal electrodes comprising a metallic powder as a conductor on ceramic green sheets, laminating the resultant sheets and firing the laminated sheets. As the conductive powder for the internal electrodes, a noble metal, such as palladium (Pd) or silver (Ag), nickel (Ni), copper (Cu) or the like is usually used, since it is fired at a temperature as high as 1000.degree. C. or above. However, such a metallic conductive powder that it undergoes volume expansion due to oxidation during firing, thereby generating cracks in the ceramic material. As described, for example, in Japanese Patent Publication No. 936/1981, Pd powder begins oxidation and expansion at about 500.degree. C., which is lower than the sintering temperature of the ordinary ceramics, reaches a maximum oxidation rate at about 800.degree. C. and thereafter is rapidly reduced to return to the original Pd at 850.degree. C. In particular, fine Pd powder has a high oxidation activity and oxidizes almost completely to cause an increase in its weight by about 15%. Since the ceramic material is poor in strength due to insufficient sintering at a temperature as low as 600.degree. to 700.degree. C., the oxidation and reduction of the internal electrodes have readily caused such structural defects as cracks and delamination.
The generation of cracks is further accelerated by an increase in the number of the multilayered ceramic layers, since this increase is accompanied by a decrease in the thickness of the ceramic layer and an increase in the number of electrodes.
Various attempts have been made to prevent the generation of cracks by the regulation of the particle size of the metallic powder, oxidation treatment or surface treatment of the powder, compounding of additives, and the like. However, an urgent requirement in recent years for the size reduction and capacitance enhancement of capacitors has resulted in decreases in the thickness of the ceramic layer and the internal electrode layer and in the areas thereof and an increase in the number of laminated layers, thus making it difficult to eliminate the above-mentioned defects, especially the cracks by the conventional methods.